[Linux-ia64] Re: 64 Bits DMA Addresses for Alloc Consistent Interfaces.

Colin Ngam
2003-05-16T00:36:55Z

"David S. Miller" wrote:

> From: Colin Ngam <cngam@sgi.com>
> Date: Thu, 15 May 2003 18:57:09 -0500
>
> It is in the PCI-X Spec that all PCI-X devices in PCI-X Mode have
> to support DAC.
>
> Having to support DAC cycles does not mean that it must support full
> 64-bit DMA addresses in it's descriptors.

Hi David,

I do not believe it is within spec to perform DAC when the
Upper 32bits are 0s. Current usage of pci_alloc_consistent(),
even if you want to do DAC, you cannot, because the interface
is defined to return only 32bits worth of addresses.

However, I think we are beyond this point now.

Thanks.

colin

>
>
> A cost sensitive PCI-X device may wish to use 32-bit addressing in
> it's descriptors in order to keep pin counts down etc.